>Number:         8364
>Category:       port-i386
>Synopsis:       egcs optimizer bug on i386 tickled by rwho
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-i386-maintainer (NetBSD/i386 Portmaster)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Sep  9 14:35:01 1999
>Last-Modified:
>Originator:     John Darrow
>Organization:
	Computing Services
	Wheaton College, Wheaton, IL
>Release:        from the egcs integration to at least current-19990909, including 1.4*
>Environment:
System: NetBSD jdarrowp5.wheaton.edu 1.4K NetBSD 1.4K (JDARROWP5) #0: Thu Sep 9 13:13:41 CDT 1999 jdarrow@jdarrowp5.wheaton.edu:/var/src/sys/arch/i386/compile/JDARROWP5 i386


>Description:
	egcs on i386 has an optimizer bug which happens to get hit by rwho.
	(Id: NetBSD: rwho.c,v 1.11 1998/12/19 21:52:00 christos Exp )

	rwho uses an idle counter mp->myidle which is originally in seconds.
	It then divides it by 60 (rwho.c line 168) to get a counter in minutes.
	If the counter is >= 60, it prints out in hours and minutes, the
	former being mp->myidle / 60 (rwho.c line 174).

	When -O2 is used, the optimizer somehow attempts to (mis-)combine the 
	two divisions by 60, resulting in strange (negative) output for the
	hours part of the idle time (while the minutes remains correct).
	With -O, the output is correct.

	Adding a printf of mp->myidle between lines 168 and 169 somehow
	"fixes" the problem, as does adding a printf of mp->myidle / 60
	before line 173.  Adding a simple printf of mp->myidle before 173
	does not, however.  Also, breaking the division in line 168 into
	two divisions (say, first by 10 then by 6) also "fixes" the problem.
>How-To-Repeat:

[60] root@jdarrowp5:ttyp4:/var/src/usr.bin/rwho:# !make
make cleandir depend CFLAGS=-O2 all     
rm -f a.out [Ee]rrs mklog core *.core  rwho rwho.o  rwho.ln
rm -f rwho.cat1    
rm -f .depend /var/src/usr.bin/rwho/tags 
mkdep -a rwho.c    
cc -O2  -c rwho.c                        
cc   -o rwho rwho.o                      
nroff -Tascii -mandoc rwho.1 > rwho.cat1 
[61] root@jdarrowp5:ttyp4:/var/src/usr.bin/rwho:# ./rwho -a
dlang    johnh:ttyp1      Sep  9 15:32   
eenke    csserver2:ttyp1  Sep  9 15:37   :09
eenke    csserver2:ttyp2  Sep  9 14:57   :49
eenke    csserver2:ttyp3  Sep  9 14:57   
eenke    scilab1:ttyp1    Sep  9 12:49 -5:35
jdarrow  csserver2:ttyp4  Sep  9 15:01   :09
jdarrow  csserver2:ttyp8  Sep  8 21:19 -6:05
jdarrow  jdarrowppp:tty02 Sep  7 23:04   :03
jdarrow  jdarrowp5:ttyp1  Sep  9 13:44   :08
jdarrow  jdarrowp5:ttyp2  Sep  9 13:44   
jdarrow  jdarrowp5:ttyp3  Sep  9 13:44 -4:01
jdarrow  jdarrowp5:ttyp4  Sep  9 13:44   
jdarrow  jdarrowp5:ttyp5  Sep  9 13:44 -4:01
johnh    csserver2:ttyp6  Sep  9 14:25 -3:20
johnh    johnh:ttyp2      Aug 23 07:14 -3:34
johnh    johnh:ttyp3      Sep  2 15:04   :22
johnh    johnh:ttyp5      Sep  9 14:20 -3:20
mangliss johnh:ttyp6      Sep  9 15:06   
mangliss johnh:ttyp8      Sep  9 15:12   :15
peapen   johnh:ttyp4      Sep  9 15:06   
[62] root@jdarrowp5:ttyp4:/var/src/usr.bin/rwho:# make cleandir depend CFLAGS=-O
 all                                     
rm -f a.out [Ee]rrs mklog core *.core  rwho rwho.o  rwho.ln
rm -f rwho.cat1    
rm -f .depend /var/src/usr.bin/rwho/tags 
mkdep -a rwho.c    
cc -O  -c rwho.c   
cc   -o rwho rwho.o                      
nroff -Tascii -mandoc rwho.1 > rwho.cat1 
[63] root@jdarrowp5:ttyp4:/var/src/usr.bin/rwho:# ./rwho -a
dlang    johnh:ttyp1      Sep  9 15:32
eenke    csserver2:ttyp1  Sep  9 15:37   :09
eenke    csserver2:ttyp2  Sep  9 14:57   :49
eenke    csserver2:ttyp3  Sep  9 14:57
eenke    scilab1:ttyp1    Sep  9 12:49  2:35
jdarrow  csserver2:ttyp4  Sep  9 15:01   :09
jdarrow  csserver2:ttyp8  Sep  8 21:19  3:05
jdarrow  jdarrowppp:tty02 Sep  7 23:04   :03
jdarrow  jdarrowp5:ttyp1  Sep  9 13:44   :08
jdarrow  jdarrowp5:ttyp2  Sep  9 13:44
jdarrow  jdarrowp5:ttyp3  Sep  9 13:44  2:01
jdarrow  jdarrowp5:ttyp4  Sep  9 13:44
jdarrow  jdarrowp5:ttyp5  Sep  9 13:44  2:01
johnh    csserver2:ttyp6  Sep  9 14:25  1:20
johnh    johnh:ttyp2      Aug 23 07:14  1:34
johnh    johnh:ttyp3      Sep  2 15:04   :22
johnh    johnh:ttyp5      Sep  9 14:20  1:20
mangliss johnh:ttyp6      Sep  9 15:06
mangliss johnh:ttyp8      Sep  9 15:12   :15
peapen   johnh:ttyp4      Sep  9 15:06

>Fix:
	Workarounds: compile with -O, or change one of the divisions into
	two operations.  Fix not yet known.
>Audit-Trail:
>Unformatted: